Dicing structures for semiconductor substrates and methods of fabrication thereof

ABSTRACT

Dicing structures for semiconductor substrates and methods of fabrication thereof are described. In one embodiment, a semiconductor wafer includes a first chip disposed in a substrate, a second chip disposed adjacent the first chip and disposed in the substrate, and a dicing street disposed between the first and the second chip. A first and a second metal level are disposed over the dicing street, wherein the second metal level is disposed above the first metal level. A first alignment mark is disposed in the first metal level above a first portion of the dicing street, and first metal features disposed in the second metal level above the first portion of the dicing street.

This application claims the benefit of U.S. Provisional Application No. 61/177,034, entitled “Dicing Structures for Semiconductor Substrates and Methods of Fabrication Thereof,” filed on May 11, 2009, which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to semiconductor substrates, and more particularly to dicing structures for semiconductor structures and methods of fabrication thereof.

BACKGROUND

Semiconductor devices are used in many electronic and other applications. Semiconductor devices comprise integrated circuits that are formed on semiconductor wafers by depositing many types of thin films of material over the semiconductor wafers and patterning the thin films of material to form the integrated circuits.

Metallization layers are usually the top-most layers of semiconductor devices. While some integrated circuits have a single top layer of metallization, other integrated circuits comprise multi-level interconnects, wherein two or more metallization layers are formed over a semiconductor wafer or workpiece. Each conductive line layer typically comprises a plurality of conductive lines separated from one another by an insulating material, also referred to as an inter-level dielectric (ILD). Advanced semiconductor processes utilize inter-level dielectrics with low dielectric constants (k) and/or ultra-low dielectric constants (ULK) to minimize interconnect parasitic capacitances.

One of the challenges in semiconductor technology requires developing technologies with good product yield and reliability. However, with low dielectric constants, materials have poor mechanical properties. Consequently, use of low-k and ultra-low dielectric constant materials introduces additional challenges in maintaining yield and component reliability.

Thus, what is needed in the art are semiconductor components containing low-k and ultra-low dielectric constant materials but without comprising product yield or component reliability.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention.

Embodiments of the invention include dicing structures for semiconductor substrates. In accordance with an embodiment of the present invention, a semiconductor wafer comprises a first chip disposed in a substrate, a second chip disposed adjacent the first chip and disposed in the substrate, and a dicing street disposed between the first and the second chip. A first and a second metal level are disposed over the dicing street, wherein the second metal level is disposed above the first metal level. A first alignment mark is disposed in the first metal level above a first portion of the dicing street, and first metal features disposed in the second metal level above the first portion of the dicing street.

The foregoing has outlined rather broadly the features of an embodiment of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of embodiments of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1, which includes FIGS. 1 a-1 f, illustrates a dicing street disposed between multiple chips on a semiconductor wafer in accordance with an embodiment of the invention, wherein FIG. 1 a illustrates a top view, FIG. 1 b is a cross-sectional view of the semiconductor around a dicing street, wherein FIGS. 1 c-1 e illustrate top cross-sectional views of metal lines within a metallization level in the dicing street, and wherein FIG. 1 f is a cross-sectional view of the semiconductor along a dicing street;

FIG. 2 illustrates a top cross-sectional view of a metal level within a dicing street, the metal level disposed immediately above a metal level comprising the alignment mark, in accordance with an embodiment of the invention;

FIG. 3, which includes FIGS. 3 a-3 c, illustrates a metallization layer above the alignment mark, in accordance with embodiments of the invention;

FIG. 4 illustrates a cross-sectional view of a dicing street in accordance with an embodiment of the invention, wherein the metal features disposed above the alignment mark are staggered between the metal levels;

FIG. 5 illustrates an alternative embodiment wherein the alignment mark is disposed in the fifth metal level M5;

FIG. 6 illustrates an alternative embodiment wherein the alignment mark is disposed in the fifth metal level M5, wherein at least some of the metal levels below the alignment mark comprise metal features;

FIG. 7, which includes FIGS. 7 a-7 d, illustrates an embodiment of the invention wherein the alignment mark is formed in multiple metal levels;

FIG. 8, which includes FIGS. 8 a-8 d, illustrates an embodiment of the invention wherein the alignment mark is formed in multiple metal levels;

FIG. 9 illustrates a method of designing second metal features below an alignment mark in accordance with embodiments of the invention;

FIG. 10, which includes FIGS. 10 a-10 c, illustrates a cross-sectional view of the dicing street during the design of the dicing street illustrated in FIG. 9, in accordance with embodiments of the invention; and

FIG. 11, which includes FIGS. 11 a-11 c, illustrates a method of fabrication of the chips in accordance with an embodiment of the invention.

Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to embodiments in a specific context, namely to structures within dicing regions of a semiconductor substrate. The invention may also be applied, however, to other types of structures outside the dicing regions, for example, to improve mechanical reliability.

Low-k dielectric materials are used to lower parasitic interconnect capacitances in BEOL or metallization levels. Recent and future technology will likely introduce further lower dielectric constant materials such as ultra low-k dielectric materials. However, the introduction of such materials introduces a number of challenges. For example, low-k materials typically comprise poor mechanical properties. Further, adhesion of these low-k dielectric material layers to adjacent dielectric layers and metal layers is poor. Consequently, low-k dielectric layers are prone to cracks and/or delaminations. Such failure can arise either during processing or during operation of the chip. For example, after the deposition of these low-k dielectric material layers, cracks may develop during subsequent processing of the semiconductor wafer.

A significant source of cracks arises from the corners and the edges of the chips either from stress concentrations in the edges or from other mechanical impact. For example, stresses induced in the edge of the chip during wafer dicing may create micro-cracks and propagate rapidly through the dielectric layers. One way to minimize such micro-crack propagation is the use of a crack-stop structure. The crack-stop structure is a metal wall (a combination of metal lines and vias over many metallization levels) introduced around the periphery of a chip. However, crack stop structures do not ensure complete immunity. For example, large cracks may possess sufficient energy to delaminate the crack stop structure or to break through weak spots in the crack stop structures.

In various embodiments, the present invention prevents crack propagation during wafer dicing by introducing additional features within the region used for dicing. Additional structures added to the dicing region may interfere with alignment mark detection units necessary to align the wafer correctly with a dicing tool. However, in various embodiments, the invention overcomes these limitations by the selective use of additional features to minimize aligning errors during dicing.

A structural embodiment of a dicing street for separating multiple chips fabricated on a semiconductor substrate is described using FIG. 1. Further structural embodiments of the dicing street will be described with respect to FIGS. 2-8. A method of designing the dicing street will be described in FIGS. 9 and 10. A method of fabricating the dicing street in accordance with embodiments of the invention will be described using FIG. 11.

FIG. 1, which includes FIGS. 1 a-1 f, illustrates a semiconductor wafer after fabrication of individual chips but before dicing, in accordance with embodiments of the invention. FIG. 1 a illustrates a top view of the semiconductor wafer and illustrates multiple chips separated by dicing streets. FIG. 1 b is a cross-sectional view of the semiconductor around a dicing street. FIGS. 1 c-1 e illustrate top cross-sectional views of metal lines within a metallization level, wherein FIG. 1 c illustrates the metal lines in a metal level comprising the alignment mark, wherein FIG. 1 d illustrates the metal lines in a metal level above the alignment mark, and wherein FIG. 1 e illustrates the metal lines in a metal level below the alignment mark. FIG. 1 f is a cross-sectional view of the semiconductor along a dicing street.

FIG. 1 a illustrates a top view of a semiconductor wafer comprising a first chip 1, a second chip 2, a third chip 3, and a fourth chip 4 disposed in a substrate 10. The substrate 10 comprises active devices forming the active circuitry of each of the semiconductor chip. The active circuitry contains the active device regions and includes necessary transistors, resistors, capacitors, inductors or other components used to form integrated circuits. For example, active areas that include transistors (e.g., CMOS transistors) can be separated from one another by isolation regions, e.g., shallow trench isolations.

Each of the chips on the substrate 10 comprises metallization levels formed over the active device regions to electrically contact and interconnect the active devices. The metallization and active device regions together form a completed functional integrated circuit. In other words, the electrical functions of the first, the second, the third, and the fourth chips 1-4 can be performed by the interconnected active circuitry.

The first, the second, the third, and the fourth chips 1-4 are separated by dicing streets 11. The dicing streets 11 comprise alignment marks 21 for dicing as well as other structures such as test and monitoring structures. Dicing streets 11 are typically about 10 μm to about 300 μm wide. The first, the second, the third, and the fourth chips 1-4 are surrounded by crack stop structures (not shown) that prevent cracks from propagating from the dicing street 11 into the first, the second, the third, and the fourth chips 1-4.

FIG. 1 b illustrates a vertical cross-section (line 1 b-1 b of FIG. 1 a) of a portion of the wafer 15 (ellipse) illustrated in FIG. 1 a. While only the dicing street 11 between the first and the second chips 1 and 2 is illustrated in FIG. 1 b, other dicing streets between other chips (for example, between the third and the fourth chips 3 and 4) are similar. FIG. 1 b illustrates the edge of the first and the second chips 1 and 2. The edge of the first and the second chips 1 and 2 may include structures such as a crack stop structure (not shown), as well as other structures such as a moisture barrier.

As illustrated in FIG. 1 b, a back end of the line (BEOL) layer 20 is disposed above the substrate 10. The BEOL layer comprises the metal levels and corresponding via levels. The metal lines connect the various active devices on the chip, whereas the vias connect the different metal levels. In various embodiments, the metal lines and vias comprise an inner metal core and an outer metal liner. The inner metal core comprises copper, although other metals may also be used in some embodiments. In some embodiments, the metal lines comprise tungsten and/or aluminum. The outer metal liner comprises a barrier metal such as TiN or TaN (or any other suitable metal liner materials).

Each metal level comprises metal lines embedded in an inter-level dielectric layer 41. The BEOL layer 20 comprises multiple layers of the inter-level dielectric layer 41. The inter-level dielectric layer 41 comprises a low-k dielectric material such as a material selected from the group comprising fluorinated silicate glass (FSG), carbon doped glass, organo silicate glass (OSG), hydrogen doped glass, porous carbon doped glass, porous silicon dioxide, polymeric dielectrics, F-doped amorphous carbon, silicone based polymeric dielectrics such as hydrogen silsesquioxane (HSQ) and methylsilsesquioxane (MSQ). In some embodiments, the inter-level dielectric layer 41 comprises ultra low-k materials such as porous silicate glass, xerogel, aerogel, nano clustered silica (NCS), porous organo silicate glass, and porous organics. In some embodiments, the top layers of the inter-level dielectric layer 41 comprises a higher-k dielectric such as SiO2 or FSG. The interconnect stack in the BEOL layers 20 may comprise any combination of the above dielectric materials.

In various embodiments, the BEOL layer 20 comprises multiple layers of the inter-level dielectric layer 41 separated by etch stop liners. The etch stop liners comprise a material comprising SiCHN although, in other embodiments, other nitrides or other suitable materials may be used. Examples of etch stop liners include materials such as silicon nitride (SiN), silicon oxynitride (SiON), silicon carbide (SiC) or silicon carbo nitride (SiCN).

In various embodiments, the BEOL layers 20 are covered by a passivation layer 50, and may comprise additional features for contacting the upper metallization levels. For example, contact pads are disposed in the passivation layer 50 to electrically contact the metallization levels. In logic devices, the metallization may include many layers, e.g., nine or more, of copper or alternatively of other metals. In memory devices, such as DRAMs, the number of metal levels may be less and they may comprise aluminum metal lines.

The dicing street comprises an alignment mark 21. For example, in one embodiment, the alignment mark 21 is disposed in the third metal level M3. However, in other embodiments, the alignment mark 21 is disposed in other metal levels. Alignment marks are used for aligning the substrate 10, for example, the wafer with a dicing tool. An interferometer may be used to detect the alignment mark 21, using for example, a difference in contrast between the alignment mark 21 and the background substrate 10.

In various embodiments, the dicing street 11 also comprises metal lines. As illustrated in FIG. 1 b, the metal levels disposed above the alignment mark 21 comprise metal lines, whereas a metal level disposed immediately below the alignment mark 21 does not comprise any metal lines. In some embodiments, all metal levels below the alignment mark 21 do not comprise any metal lines.

Metal lines disposed in metal levels above the alignment mark 21 do not significantly produce an erroneous reading during the alignment process. In contrast, metal lines disposed in metal levels below the alignment mark 21 produce an erroneous reading during the alignment process. Hence, in various embodiments, the invention minimizes errors in aligning the substrate by not including metal levels immediately below the alignment mark. In various embodiments, the mechanical properties of the BEOL layer 20 above the dicing street is significantly improved by including metal lines above the alignment mark 21. The improved mechanical strength minimizes crack propagation or delamination, while minimizing misalignment errors.

FIGS. 1 c-1 e illustrate top cross-sectional views of the dicing street illustrating metal lines. Referring to FIG. 1 c, the third metal level M3 within the dicing street 11 comprises an alignment mark 21. The alignment mark 21 is disposed in the inter-level dielectric layer 41.

FIG. 1 d illustrates the metal level (fourth metal level M4) immediately above the alignment mark 21. The fourth metal level M4 disposed within the first or second chips 1 or 2 comprises first metal features 42, whereas the fourth metal level M4 disposed within the dicing street 11 comprises second metal features 43. The first metal features 42 include metal lines coupling active devices as well as metal lines used in forming capacitor, crack stop or moisture barrier structures.

In various embodiments, the first metal features 42 and the second metal features 43 comprise the same material layers. However, the shapes and sizes of the first metal features 42 and the second metal features 43 may be different. Similarly, the areal density of the second metal features 43 may be different than the first metal features 42. In one embodiment, the second metal features 43 comprise a square shape, whereas on other embodiments, any suitable shape such as circular, elliptical, or rectangular shape may be used.

FIG. 1 e illustrates the metal level (second metal level M2) immediately below the alignment mark 21. The second metal level M2 disposed within the first or second chips 1 or 2 comprise first metal features 42. Unlike the fourth metal level M4, the second metal level M2 disposed within the dicing street 11 does not comprise any metal features. The absence of metal lines below the alignment mark minimizes photo interference noise when aligning the substrate 10 with a dicing tool.

FIG. 1 f illustrates a vertical cross-section (line 1 f-1 f of FIG. 1 a) along the dicing street 11. As illustrated in FIG. 1 f, the metal levels disposed above the alignment mark 21 comprise metal lines, whereas a metal level disposed immediately below the alignment mark 21 does not comprise any metal lines. In the illustrated embodiment, all metal levels below the alignment mark 21 do not comprise any metal lines.

FIG. 2 illustrates a top cross-sectional view of a metal level within a dicing street disposed immediately above a metal level comprising the alignment mark, in accordance with an embodiment of the invention.

FIG. 2 illustrates an embodiment in which the layer above the alignment mark comprises metal features that are optimized to minimize crack generation and/or propagation. The total surface area of the second metal feature 43 is determined by the total number of second metal features 43 and the area of each of the second metal features 43. The distance W between the second metal features 43 along with the total surface area of the second metal features 43 determines the metal density (ratio of the total surface area of the second metal features 43 to the total surface area of the metal level). As the metal density increases towards about 100% or decreases towards about 0%, the tendency to form micro-cracks and/or delaminate increases during dicing. In various embodiments, this metal density is about 20% to about 50%, and about 30% to about 40% in one embodiment. Referring to FIG. 2, the second metal features comprise a square shaped metal line.

FIG. 3, which includes FIGS. 3 a-3 c, illustrates a metallization layer above the alignment mark, in accordance with embodiments of the invention.

Referring to FIG. 3 a, second metal features 43 comprising metal lines are disposed in the layer above the alignment mark. Unlike the prior embodiment, the second metal features 43 in this embodiment comprise rectangular lines disposed within an inter-level dielectric layer 41.

FIG. 3 b illustrates an alternative embodiment, wherein the second metal features 43 comprise different shapes and are spaced in a pattern. In one embodiment, the rectangular line like features of the second metal features 43 are placed along the periphery of the dicing street whereas the smaller second metal features 43 are placed towards the central region of the dicing street. FIG. 3 c illustrates an alternative embodiment, wherein line shaped second metal features 43 are placed centrally while smaller second metal features 43 are placed towards the periphery of the dicing street. The embodiments of FIG. 3 b or 3 c may be experimentally chosen and may depend on the inter-level dielectric layer 41 as well as the type of the dicing tool. Further, subsequent metal levels may have second metal features 43 arranged in a different pattern.

FIG. 4 illustrates a cross-sectional view of a dicing street in accordance with an embodiment of the invention, wherein the metal features disposed above the alignment mark are staggered between the metal levels.

As also illustrated in FIG. 1 b, a BEOL layer 20 is disposed above the substrate 10. The BEOL layer 20 comprises the metal levels and corresponding via levels. An alignment mark 21 is disposed within the BEOL layer 20. The metal levels disposed above the alignment mark 21 comprise metal lines, whereas metal levels disposed below the alignment mark 21 do not comprise any metal lines.

Referring to FIG. 4, the metal level disposed immediately above any metal level is staggered. For example, second metal features 43 in the fourth metal level M4 are displaced laterally by a distance D (staggered) relative to second metal features 43 in the fifth metal level M5. Second metal features 43 in the sixth metal level M6 are also displaced laterally relative to the second metal features 43 in the fifth metal level M5. Hence, second metal features 43 in the fourth metal level M4 and the sixth metal level M6 are positioned above each other. Similarly, second metal features 43 in the fifth metal level M5 are disposed below the second metal features 43 in the seventh and ninth metal levels M7 and M9.

FIG. 5 illustrates an alternative embodiment wherein the alignment mark 21 is disposed in the fifth metal level M5. Metal levels above the alignment mark 21 comprise second metal features 43. Hence, sixth, seventh, eighth, and ninth metal levels M6, M7, M8 and M9 include the second metal features 43. However, metal levels below the alignment mark 21 do not include the second metal features 43.

FIG. 6 illustrates an alternative embodiment wherein the alignment mark 21 is disposed in the fifth metal level M5, wherein at least some of the metal levels below the alignment mark 21 comprise metal features. As in the prior embodiment, metal levels above the alignment mark 21 comprise second metal features 43. Hence, sixth, seventh, eighth, and ninth metal levels M6, M7, M8 and M9 include the second metal features 43. However, unlike the prior embodiment, some of the metal levels below the alignment mark 21 include the second metal features 43. In particular, the fourth metal level M4 which is immediately below the alignment mark 21 does not include second metal features 43, whereas metal levels much below the alignment mark, e.g., first metal level M1 includes the second metal features 43. This is possible because the metal level immediately underneath the alignment mark introduces the most interference noise during the aligning process. The noise generated from lower metal levels decreases with distance from the alignment mark 21. Hence, the lowest metal level may include second metal features 43.

FIG. 7, which includes FIGS. 7 a-7 d, illustrates an embodiment of the invention wherein the alignment mark is formed in multiple metal levels.

FIG. 7 a illustrates a top view of a semiconductor wafer comprising a first chip 1, a second chip 2, a third chip 3, and a fourth chip 4 disposed in a substrate 10 (as described in FIG. 1 a). The first, the second, the third, and the fourth chips 1-4 are separated by dicing streets 11, which include alignment mark 21. As illustrated in FIG. 7 a, the alignment mark 21 has four corners or edges, two of which are parallel to the perimeter of the first and the second chip, while two of the corners are perpendicular to the perimeter of the first and the second chip. The cross-sectional view of the dicing street 11 along the line 7 b-7 b is illustrated in FIG. 7 b. The alignment marks 21 include a first alignment mark 21 a, a second alignment mark 21 b, a third alignment mark 21 c, a fourth alignment mark 21 d, and a fifth alignment mark 21 e.

Referring to FIG. 7 b, the first alignment mark 21 a is disposed in the third metal level, the second alignment mark 21 b is disposed in the seventh metal level, the third alignment mark 21 c is disposed in the ninth metal level, the fourth alignment mark 21 d is disposed in the sixth metal level, and the fifth alignment mark 21 e is disposed in the second metal level. As illustrated in FIG. 7 b, second metal features 43 are disposed above the alignment marks 21 but not below the alignment marks 21. Further, portions of the alignment marks disposed in the upper metal levels are centrally placed enabling portions of the first alignment mark 21 disposed in the lower metal levels to be placed along the edges. For example, third alignment mark 21 c is towards the inner region of the dicing street 11, whereas the first and the seventh alignment marks 21 a and 21 e are placed along the edges of the dicing street 11.

Alignment marks 21 disposed in the lower metal levels, e.g., the first and the fifth alignment marks 21 a and 21 e, provide better protection to crack propagation and initiation because of the larger metal density. Alignment marks disposed in the upper metal levels, e.g., the third alignment mark 21 c, provide minimal protection to crack nucleation or propagation. In various embodiments, weaker portions of the alignment marks are formed centrally and the stronger portions of the alignment mark are formed along the corners of the dicing street 11.

FIG. 7 c illustrates an alternative embodiment of the alignment mark described in FIG. 7 b. However, unlike the prior embodiment, at least some of the lower metal levels underneath some of the alignment marks comprise secondary metal features 43. In one embodiment, for each alignment mark only a few metal levels below it are empty. For example, in FIG. 7 c, for the third alignment mark 21 c, the lower metal levels in the fourth, fifth, sixth, seventh, and eighth metal levels M4, M5, M6, M7, and M8 do not comprise secondary metal features 43, while the first, second, and third metal levels M1, M2, and M3 comprise secondary metal features 43. While in this embodiment, five alignment marks are shown, in different embodiments, more or fewer alignment marks may be used. Further, all the alignment marks may not share a same cross-sectional plane in some embodiments.

FIG. 7 d illustrates a top view of a dicing street comprising alignment marks disposed in multiple metal levels in accordance with an embodiment of the invention. As illustrated in FIG. 7 d, the dicing street 11 (along line 7 b-7 b of FIG. 7 a) comprises a first alignment mark A1, a second alignment mark A2, a third alignment mark A3, a fourth alignment mark A4, a fifth alignment mark A5, a sixth alignment mark A6, a seventh alignment mark A7, an eighth alignment mark A8, a ninth alignment mark A9, and a tenth alignment mark A10 disposed in a first metal level, a second metal level, a third metal level, a fourth metal level, a fifth metal level, a sixth metal level, a seventh metal level, an eighth metal level, a ninth metal level, and a tenth metal level, respectively. The first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth alignment marks A1-A10 are formed as in prior embodiments. Hence, the first alignment mark A1 has one of the highest metal density, while the tenth alignment mark A10 has the lowest metal density amongst the alignment marks.

As illustrated in FIG. 7 d, the first and the second alignment marks A1 and A2 are disposed along the edges of the dicing street 11, whereas the eighth, the ninth, and the tenth alignment marks A8, A9 and A10 are disposed centrally. Hence, alignment marks with lower density of second metal features 43 are disposed centrally, while alignment marks with higher density of second metal features 43 are disposed along the corners of the dicing street 11.

FIG. 8, which includes FIGS. 8 a-8 d, illustrates an embodiment of the invention wherein the alignment mark is formed in multiple metal levels.

FIG. 8 a illustrates a top view of a semiconductor wafer identical to FIG. 7 a and illustrates the cutline 8 b-8 b of the cross-section illustrated in FIGS. 8 b and 8 c. This embodiment is similar to the prior embodiment except that the multiple metal levels of the alignment marks 21 are formed perpendicular to the dicing street 11. Referring to the cross-sectional view of FIG. 8 b, a first alignment mark 21 a is disposed in the third metal level, a second alignment mark 21 b is disposed in the seventh metal level, a third alignment mark 21 c is disposed in the ninth metal level, a fourth alignment mark 21 d is disposed in the sixth metal level, and a fifth alignment mark 21 e is disposed in the second metal level. As illustrated in FIG. 8 b, second metal features 43 are disposed above the alignment marks 21 but not below the alignment marks 21.

FIG. 8 c illustrates an alternative embodiment of the alignment mark described in FIG. 8 b. As in the prior embodiment described in FIG. 7 c, at least some of the lower metal levels underneath some of the alignment marks comprise secondary metal features 43.

FIG. 8 d illustrates a top view of a dicing street comprising alignment marks disposed in multiple metal levels in accordance with an embodiment of the invention. As illustrated in FIG. 8 d, the dicing street 11 in a direction perpendicular to the dicing street (along line 8 b-8 b of FIG. 8 a) comprises a first alignment mark A1, a second alignment mark A2, a third alignment mark A3, a fourth alignment mark A4, a fifth alignment mark A5, a sixth alignment mark A6, a seventh alignment mark A7, an eighth alignment mark A8, a ninth alignment mark A9, and a tenth alignment mark A10 disposed in a first metal level, a second metal level, a third metal level, a fourth metal level, a fifth metal level, a sixth metal level, a seventh metal level, an eighth metal level, a ninth metal level, and a tenth metal level respectively. The first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth alignment marks A1-A10 are formed as in prior embodiments. Hence, the first alignment mark A1 has one of the highest metal density, while the tenth alignment mark A10 has the lowest metal density amongst the alignment marks.

As illustrated in FIG. 8 d, the first and the second alignment marks A1 and A2 are disposed along the edges of the dicing street 11, whereas the eighth, the ninth, and the tenth alignment marks A8, A9 and A10 are disposed centrally. Hence, alignment marks with lower density of second metal features 43 are disposed centrally, while alignment marks with higher density of second metal features 43 are disposed along the edges of the dicing street 11.

FIG. 9 illustrates a method of designing a dicing street with second metal features in accordance with embodiments of the invention. FIG. 10, which includes FIGS. 10 a-10 c, illustrates a cross-sectional view of the dicing street during the design process.

Referring to FIG. 9, the alignment mark is designed in an nth metal level Mn (box 211). The secondary metal features are added to all metal levels above nth metal level Mn (box 212). The dicing street 11 after this stage of the design is shown in FIG. 10 a. Subsequently, the second metal features 43 are placed on all the metal levels (box 213, FIG. 10 b). The interference signal is measured (or simulated) to detect the noise level from the second metal features 43 disposed in the metal levels below the alignment mark (box 215). If the noise level is acceptable, the design is finalized (box 218), if the noise level is unacceptable, secondary metal features 43 from the highest metal level below the alignment mark are removed (box 217). The noise level of the corresponding structure is measured (box 215). This process is iteratively continued until an acceptable noise level is achieved.

In an alternative embodiment, after adding second metal features 43 to all metal levels above the nth metal level Mn (FIG. 10 a), secondary features 43 are added to the lowest metal level (e.g., first metal level M1). The noise level of the structure is measured. If the noise level does not exceed an acceptable noise level, secondary metal features 43 are added to the next available lowest metal level (e.g., second metal level M2). If the noise level exceeds the acceptable noise level, secondary metal features 43 are removed from the highest metal level below the alignment mark and the design finalized.

FIG. 11, which includes FIGS. 11 a-11 c, illustrates a method of fabrication of a substrate the multiple chips in accordance with an embodiment of the invention.

Referring to FIG. 11 a, the substrate 10 comprises a first portion for forming a first chip 1, and a second region for forming a dicing street 11. Referring to FIG. 11 a, the substrate 10 comprises a bulk mono-crystalline silicon substrate (or a layer grown thereon or otherwise formed therein), a layer of a silicon-on-insulator (SOI) wafer, or a layer of a germanium-on-insulator (GeOI) wafer. In other embodiments, other semiconductors such as silicon germanium, germanium, gallium arsenide, indium arsenide, indium gallium arsenide, indium antimonide or others, can be used with the wafer.

Isolation regions 114 are formed in the substrate 10 using conventional techniques. Referring to FIG. 11 a, active device regions 111 are formed in the region for forming the first chip 1 on a top side of a substrate 10 during front end processing. The active device regions 111 or active circuitry can include transistors, resistors, capacitors, inductors or other components used to form integrated circuits. For example, in one embodiment, active areas include transistors 113 (e.g., CMOS transistors) comprising gate lines 112, and separated from one another by isolation regions 114, e.g., shallow trench isolation. In an alternative embodiment, the active device regions 111 comprise bipolar transistors.

Referring now to FIG. 11 b, a first insulating material layer 121 is formed over the substrate 10. An etch stop liner is optionally deposited over the substrate 10 before depositing the first insulating material layer 121 to also protect the underlying substrate during contact plug formation. For example, a nitride film (e.g., silicon nitride) is deposited as an etch stop liner.

The first insulating material layer 121 comprises insulating materials typically used in semiconductor manufacturing for inter-level dielectric (ILD) layers, such as SiO2, tetra ethyl oxysilane (TEOS), fluorinated TEOS (FTEOS), doped glass (BPSG, PSG, BSG), organo silicate glass (OSG), fluorinated silicate glass (FSG), and spin-on glass (SOG), SiN, SiON. The insulating material layer 121 may also comprise suitable low-k or ultra-low-k (ULK) materials. The first insulating material layer 121 may comprise a thickness of about 500 nm or less in one embodiment.

Contact plugs 122 are formed within the insulating material layer 121 for coupling the transistor 113 to other devices or external contacts. A second insulating material layer 131 is then deposited over the first insulating material layer 121. The second insulating material layer 131 comprises a low-k dielectric material having a dielectric constant of 3.6 or less, and may require heating, e.g., up to 400 degrees C. to remove solvents. The second insulating material layer 131 is patterned via lithography, e.g., with a mask. A photoresist is deposited over the second insulating material layer 131, and portions of the photoresist are exposed, developed and removed, leaving a pattern for a metal line. The exposed second insulating material layer 131 is removed to form an opening in the second insulating material layer 131.

The opening is filled with a conductive material, for example, using an electroplated fill process to form a first metal level (M1) having a portion residing within the second insulating material layer 131 and a portion residing over the first insulating material layer 121. First metal features 42 are formed in the first metal line level (M1) by filling the openings in the second insulating material layer 131. Based on the design of the dicing street region (for example, as described in FIG. 9), second metal features 43 may also be formed in the first metal line level (M1) by filling the openings in the second insulating material layer 131. In particular, the first metal features 42 are formed in the chip 1 region, whereas second metal features 43 are formed in the dicing street 11 region. In various embodiments, the conductive material comprises copper, aluminum or other metals or combinations thereof.

Before depositing the conductive material, a conductive liner is optionally deposited using a conformal deposition process, leaving a conformal liner or diffusion barrier along the interior walls of the opening of second insulating material layer 131. In one embodiment, the conductive liner comprises tantalum nitride deposited by plasma vapor deposition (PVD). Alternatively, the conductive liner may comprise titanium nitride, tungsten nitride, a refractory metal or other barrier layers that may be conformally deposited, for example, using CVD, PVD processes or electro-less plating. The conductive liner may comprise a bi-layer of material, including, for example, a barrier layer and a conformal seed layer, which comprises copper, aluminum, other metals or combinations thereof. The seed layer may be deposited using a CVD process, for example.

A third insulating material layer 141 is deposited over the second insulating material layer 131. The third insulating material layer 141 in the first chip 1 region is patterned and etched to create via holes. In some embodiments, the third insulating material layer 141 in the dicing street 11 region is not patterned to form via holes. The via holes formed in the first chip region 1 are filled with another conductive material such as copper to form first via level (V1) comprising vias 142.

Similarly, more metal levels and via levels are formed above the first via level (V1) by repeating the process for formation of metal lines and vias. For example, in FIG. 11 b, fourth, fifth, sixth, seventh, and eighth insulating material layers 151, 161, 171, 181, and 191 comprising second metal level (M2), second via level (V2), third metal level (M3), third via level (V3), and fourth metal level (M4) are formed.

As illustrated in FIG. 11 b, the alignment mark 21 is formed in one of the metal levels. In one embodiment, the alignment mark 21 is formed in the third metal level. Hence, no second metal features 43 are formed in the second metal level M2 of the dicing street, whereas the fourth metal level M4 comprises second metal features 43.

As next illustrated in FIG. 11 c, subsequent metal levels are formed. For example, top metal level M5 is formed in a tenth insulating material layer 211 disposed over a ninth insulating layer 201. A passivation layer 50 is deposited over the last metal line (top metal level M5). The passivation layer 50 comprises an oxide layer or an oxide/nitride layer stack. In some embodiments, the passivation layer 50 comprises silicon nitride, or silicon oxynitride, FTEOS, SiCOH, or combinations thereof with polyimide, photoimide, BCB or other organic polymers.

After all front end and back end processing, the substrate 10 is mounted on a dicing tape or a holder for support during subsequent dicing. A dicer (not shown) is aligned using alignment mark 21 to the dicing street 11. As the second metal features 43 are not formed under the alignment marks 21, minimal noise is generated, minimizing alignment errors. The presence of second metal features 43 above the alignment marks 21 reduces crack initiation. The dicer cuts through the BEOL layers 20 and the substrate 10. Individual dies are generated after the dicing process. In various embodiments, dicing is performed by mechanical sawing, by scribing and then breaking or by laser cutting. The die is extracted by die handling equipment from the dicing tape, like a die bonder or die sorter, forming individual chips.

Following the dicing process, the individual chips are encapsulated into packages which are then suitable for use in building electronic devices such as computers, etc. The chips are integrated into a lead-frame package or placed directly on a PC board substrate or packaged using solder bumping technologies.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, it will be readily understood by those skilled in the art that many of the features, functions, processes, and materials described herein may be varied while remaining within the scope of the present invention.

Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 

What is claimed is:
 1. A semiconductor wafer comprising: a first chip disposed in a substrate; a second chip disposed adjacent the first chip and disposed in the substrate; a dicing street disposed between the first and the second chip; a first and a second metal level disposed over the dicing street, the first metal level and the second metal level each comprising at least a dielectric layer, the second metal level disposed on the first metal level; at least one first alignment mark disposed in the first metal level above a first portion of the dicing street, the at least one first alignment mark having a substantially flat uppermost surface extending contiguously between lateral boundaries of the at least one first alignment mark, the uppermost surface of the at least one alignment mark substantially level with the uppermost surface of the dielectric layer of the first metal level; first metal features disposed in the second metal level above the first portion of the dicing street, a plurality of the first metal features laterally separated by first distances and a portion of each of at least two of the first metal features aligned over and within the lateral boundaries of a same one of the at least one first alignment mark, the plurality of the first metal features disposed in a plurality of rows; and a third metal level comprising a third dielectric material extending contiguously from an uppermost surface to a bottommost surface of the third metal level, and having a bottommost surface in direct physical contact with an uppermost surface of the at least a dielectric layer of the second metal level, wherein a portion of each of a plurality of second metal features of the third metal level is aligned directly over and within lateral boundaries of the first alignment mark.
 2. The wafer of claim 1, wherein the first metal features comprise square or rectangular shaped metal lines.
 3. The wafer of claim 1, wherein the total surface area of the first metal features divided by the total surface area of the first portion of the dicing street is about 20% to about 50%.
 4. The wafer of claim 1, further comprising a fourth metal level disposed immediately under the first metal level and comprising no metal features above the first portion of the dicing street.
 5. The wafer of claim 4, further comprising: a fourth metal level disposed immediately under the third metal level, the fourth metal level being disposed over the dicing street, the fourth metal level comprising second metal features above the first portion of the dicing street.
 6. The wafer of claim 1, further comprising: a fourth and fifth metal level disposed over the dicing street, the fourth and fifth metal levels being disposed above the first and the second metal levels, the fifth metal level disposed immediately above the fourth metal level; and a second alignment mark disposed in the fifth metal level above a second portion of the dicing street, wherein the fourth metal level comprises no metal features above the second portion of the dicing street.
 7. The wafer of claim 6, wherein the at least one first alignment mark is closer to an edge of the dicing street than the second alignment mark.
 8. The wafer of claim 6, further comprising: a sixth metal level disposed over the dicing street, the sixth metal level being disposed above the fourth and fifth metal levels; and second metal features disposed in the sixth metal level above the second portion of the dicing street.
 9. The wafer of claim 6, further comprising: a sixth, a seventh and an eighth metal level disposed over the dicing street, the sixth, the seventh and the eighth metal levels being disposed above the fourth and fifth metal levels, the eighth metal level disposed immediately above the seventh metal level, the seventh metal level disposed above the sixth metal level; a third alignment mark disposed in the eighth metal level above a third portion of the dicing street, wherein the seventh metal level comprises no metal features above the third portion of the dicing street; and second metal features disposed in the sixth metal level above the second portion of the dicing street.
 10. The wafer of claim 9, further comprising: third metal features disposed in the first metal level above the third portion of the dicing street.
 11. The wafer of claim 9, wherein the first portion of the dicing street is closer to an edge of the dicing street than the second portion of the dicing street, and wherein the second portion of the dicing street is closer to an edge of the dicing street than the third portion of the dicing street.
 12. A semiconductor wafer comprising: a substrate; a dicing street disposed in the substrate; a first metal level disposed over the dicing street and comprising a first dielectric layer extending contiguously from an uppermost surface of the first metal level to a bottommost surface of the first metal level; a first alignment mark comprising a metal and disposed in the first metal level, the at least one first alignment mark having a substantially flat uppermost surface extending laterally and contiguously between lateral boundaries of the at least one first alignment mark, the uppermost surface of the at least one alignment mark substantially level with the uppermost surface of the first dielectric layer; a second metal level disposed on the first metal level and comprising a second dielectric material extending contiguously from an uppermost surface of the second metal level to a bottommost surface of the second metal level, the second dielectric material having a bottommost surface in direct physical contact with an uppermost surface of the first dielectric layer; a plurality of first metal features disposed in the second metal level and separated by first distances, a portion of each of at least two of the plurality of first metal features aligned over and within lateral boundaries of the first alignment mark, the first alignment mark extending under a space between the at least two of the plurality of first metal features; and a third metal level disposed on the second metal level and having a plurality of second metal features disposed in a third dielectric material extending contiguously from an uppermost surface of the third metal level to a bottommost surface of the third metal level, the third dielectric material having a bottommost surface in direct physical contact with an uppermost surface of the second dielectric material, a portion of each of the plurality of second metal features aligned directly over and within lateral boundaries of the first alignment mark.
 13. The semiconductor wafer of claim 12, further comprising a fourth metal level disposed immediately under the first metal level and having no metal features aligned below the first alignment mark.
 14. The semiconductor wafer of claim 12, wherein the plurality of first metal features is disposed in a plurality of rows, each row of the plurality of rows each aligned in a first direction, each row of the plurality of rows adjacent to at least one other row in a second direction different from the first direction, each of the plurality of rows having two or more of the plurality of first metal features disposed therein and separated in the first direction by first distances.
 15. The semiconductor wafer of claim 14, wherein the metal density of the first metal features in the dicing street is about 30% to about 40%.
 16. A substrate comprising: a dicing street; a first metal level comprising a first dielectric layer and being disposed over the dicing street; a first alignment mark disposed in the first metal level, the first alignment mark comprising metal and having a top surface substantially planar with a top surface of a dielectric layer in which the first metal level is formed; a second metal level comprising a second dielectric layer and being disposed on the first metal level; a first plurality of first metal features disposed in the second metal level, a first group of metal features of the first plurality of first metal features disposed in a first row separated in a first direction by first distances, a second group of metal features of the first plurality of first metal features disposed in a second row and separated in the first direction by second distances, wherein a portion of each of the first plurality of first metal features is aligned over and within lateral boundaries of the first alignment mark, the first alignment mark extending contiguously under each of the first plurality of first metal features; a third metal level comprising a third dielectric material extending contiguously from an uppermost surface to a bottommost surface of the third metal level, and having a bottommost surface in direct physical contact with an uppermost surface of the second dielectric layer, wherein a portion of each of a plurality of second metal features of the third metal level is aligned directly over and within lateral boundaries of the first alignment mark; and one or more underlying metal levels disposed immediately under the first metal level, each of the one or more underlying metal levels having a region aligned below the first alignment mark free of alignment marks.
 17. The substrate of claim 16, wherein the metal features of the first group of metal features are staggered with respect to the metal features of the second group of metal features, wherein at least portions of metal features of the second group of metal features are aligned directly adjacent to spaces between metal features of the first group of metal features.
 18. The semiconductor wafer of claim 1, wherein the rows of the plurality of rows each aligned in a first direction, each row of the plurality of rows adjacent to at least one other row in a second direction, each of the rows having two or more of the plurality of the first metal features separated in the first direction by first distances, wherein the first direction and the second direction are substantially parallel to the uppermost surface of the at least one first alignment mark, and wherein the first direction is substantially perpendicular to the second direction.
 19. The substrate of claim 16, further comprising one or more underlying metal levels disposed immediately under the first metal level, each of the one or more underlying metal levels having a region aligned below the first alignment mark free of alignment marks.
 20. The substrate of claim 16, wherein the first row and the second row are substantially parallel and spaced apart in a second direction perpendicular to the first direction, wherein a first side of the first row is adjacent to and faces a second side of the second row, wherein the first side and the second side are parallel to the first direction. 